Greenfield Partners' plan to add a third level to its parking structure on Wilton Road secured key support Tuesday night, as the Zoning Board of Appeals approved a series of zoning variances sought by the National Hall owner to facilitate the expansion.

The variances will provide Greenfield exemptions from zoning regulations pertaining to setbacks, building coverage and landscaping.

Greenfield, a Norwalk-based commercial real estate firm, hopes to increase the deck's parking capacity to 130 spaces from its current total of 97 as part of its plans to revitalize the National Hall complex.

Adding the third story would raise the facility's height from approximately 15 feet to 24 feet, according to William Fitzpatrick, the lawyer for Greenfield Partners The revamp of the parking deck would also include building new stairs, a ramp to the third level and reconfiguring the plantings in front.

The proposed parking deck expansion has also received conditional approval from the Flood and Erosion Control Board, as well as backing from the Conservation Commission and the Architectural Review Board.

The project will next face scrutiny from the Planning and Zoning Commission, which must approve a site plan for the parking structure expansion to move ahead. The P&Z will likely begin its review of the site plan in mid-February, Fitzpatrick told the Westport News.

Increasing the size of its parking deck is a component of Greenfield's plan to redevelop a group of buildings that it owns on the west bank of the Saugatuck River in the town center. The landmark National Hall anchors that complex, and Greenfield plans to move its corporate headquarters to the site.

Greenfield Partners hopes to gain P&Z approval for the extra parking level before it relocates to National Hall, Fitzpatrick said. The redevelopment of the downtown landmark for office space would also require site plan approval from the P&Z.

Fitzpatrick declined to comment directly on Greenfield's likely course of action if the P&Z were to reject a site plan for the parking deck addition.

"I'm planning on getting the site plan approved for the parking garage, so we can proceed in the direction we planned," he added.

A lack of parking has loomed as a perennial concern for many merchants on the west side of the downtown Westport, where the parking structure is located. Unlike the larger segment of the town center, anchored by Main Street and several parking municipal lots, no public parking facilities exist on the west bank of the Saugatuck River.

"If this part of town is going to be developed ... I don't see how you can do this without increasing the parking," said ZBA Chairman Jim Ezzes. "And I don't see how you can increase the parking without doing this."

Along with Ezzes, board members Liz Wong, Douglas Bowen and Andrew Shapiro voted to approve the variances for the parking deck expansion. Expressing doubt about the need for more parking for the National Hall complex, Jacqueline Masumian abstained.

Last October, the P&Z approved a text amendment proposed by Greenfield that allows more office space in the Historic Design District where National Hall District is located. In January 2010, the Representative Town Meeting had overturned a similar text amendment presented by Greenfield.

The Wilton Road structure would provide parking for workers at National Hall and also serve patrons of several restaurants that Greenfield plans to bring to other buildings it owns on the property, Fitzpatrick said.

Greenfield has already agreed leases with two restaurants, Fitzpatrick added. Safita, a Middle Eastern restaurant in Fairfield, plans to open a second eatery at the onetime site of a firehouse at 6 Wilton Road. The second restaurant, specializing in sushi, would open at 12 Wilton Road, a building located yards away from National Hall.

Another restaurant tenant in the National Hall complex could open at 20 Wilton Road, the former site of the Peter Coppola hair salon, which relocated to Post Road East in 2010.